Human galanin expresses amphipathic properties that modulate its vasoreactivity in vivo

The purpose of this study was to determine whether human galanin, a pleiotropic 30-amino acid neuropeptide, expresses amphipathic properties in vitro and, if so, whether these properties modulate its vasoactive effects in the intact peripheral microcirculation. We found that human galanin aggregates in an aqueous solution and forms micelles with a critical micellar concentration (CMC) of 0.4 microM. In addition, the peptide interacted with model membrane as indicated by long and significant increase of the surface pressure of the biomimetic monolayer membrane in vitro. Interactions of human galanin with sterically stabilized phospholipid micelles (SMM) were not associated with a significant change in peptide conformation. Using intravital microscopy, we found that suffusion of human galanin alone elicited significant concentration-dependent vasoconstriction in the intact hamster cheek pouch. This response was amplified when human galanin in SSM was suffused onto the cheek pouch. The effects of human galanin alone and in SSM were mediated by galanin receptors because galantide, a galanin receptor antagonist, abrogated galanin-induced vasoconstriction. Collectively, these data show that human galanin expresses amphipathic properties in the presence of phospholipids which in turn amplifies its vasoactive effects in the intact peripheral microcirculation.     

Conformation-dependent effects of VIP on nociception in rats

The purpose of this study was to determine whether intrathecal injection of aqueous (random coil) vasoactive intestinal peptide (VIP) and VIP self-associated with sterically stabilized phospholipid micelles (alpha-helix VIP) at the lower lumbar vertebral level modulates foot withdrawal latency to low and high rate noxious radiant skin heating in anesthetized rats. We found that intrathecal random coil VIP evoked a significant bimodal, concentration-dependent response, early potent antinociception followed by hyperalgesia, during exposure to low and high rates of skin heating (P<0.05). Intrathecal alpha-helix VIP elicited a qualitatively similar response to that of random coil VIP except that the rate of decay of antinociception was faster and slower at low and high rates of skin heating, respectively. In addition, a low concentration of alpha-helix VIP evoked a potent late antinociception not observed with random coil VIP. Taken together, these data indicate that VIP modulates somatosensory processing in the lumbosacral spinal cord of rats in a complex fashion, and that this response is dependent, in part, on the conformation of VIP in the vicinity of target cells in the peripheral nervous system.     

Mass distributions of a macromolecular assembly based on electrospray ionization mass spectrometric masses of the constituent subunits

Macromolecular assemblies containing multiple protein subunits and having masses in the megadalton (MDa) range are involved in most of the functions of a living cell. Because of variation in the number and masses of subunits, macromolecular assemblies do not have a unique mass, but rather a mass distribution. The giant extracelular erythrocruorins (Ers), ∼ 3.5 MDa, comprized of at least 180 polypeptide chains, are one of the best characterized assemblies. Three-dimensional reconstructions from cryoelectron microscopic images show them to be hexagonal bilayer complexes of 12 subassemblies, each comprised of 12 globin chains, anchored to a subassembly of 36 nonglobin linker chains. We have calculated the most probable mass distributions forLumbricus andRiftia assemblies and their globin and linker subassemblies, based on theLumbricus Er stoichiometry and using accurate subunit masses obtained by electrospray ionization mass spectrometry. The expected masses ofLumbricus andRiftia Ers are 3.517 MDa and 3.284 MDa, respectively, with a possible variation of ∼ 9% due to the breadth of the mass distributions. TheLumbricus Er mass is in astonishingly good agreement with the mean of 23 known masses, 3.524 ± 0.481 MDa.     

Transmembrane domains in the functions of Fc receptors

In the present study, we use a novel method, PHDhtm, to predict the exact locations and extents of the transmembrane (TM) domains of multisubunit immunoglobulin Fc-receptors. Whereas most previous studies have used single residue hydrophobicity plots for characterizing of these domains, PHDhtm utilizes a system of neural networks and the evolutionary information contained in multiple alignments of related sequences to predict the above. Present PHDhtm application predicts TM domains of immunoglobulin Fc-receptors that in many cases differ significantly from those derived by using earlier methods. Comparisons of helical wheel projections of the presently derived TM domains from PHDhtm with those produced earlier reveal different hydrophobic moments as well as hydrophobic and hydrophilic surfaces. These differences probably alter the character of subunit association within the receptor complexes. This new algorithm can also be used for other membrane protein complexes and may advance both understanding the principles underlying such complexes formation and design of peptides that can interfere with such TM domain association so as to modulate specific cellular responses.     

EspH,a new cytoskeleton-modulating effector of enterohaemorrhagic and enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC) are closely related pathogens. During infection, EPEC and EHEC use a type III secretion system (TTSS) to translocate effector proteins into the infected cells and thereby modify specific host functions. These include transient filopodium formation which is Cdc42-dependent. Filopodia formation is followed by assembly of actin pedestals, the process enhanced by inhibition of Cdc42. We discovered that orf 18 of the enterocyte effacement locus encodes a new effector, which we termed EspH. We show that EspH is translocated efficiently into the infected cells by the TTSS and localizes beneath the EPEC microcolonies. Inactivation of espH resulted in enhanced formation of filopodia and attenuated the pedestals formation. Furthermore, overexpression of EspH resulted in strong repression of filopodium formation and heightened pedestal formation. We also demonstrate that overexpression of EspH by EHEC induces marked elongation of the typically flat pedestals. Similar pedestal elongation was seen upon infection of COS cells overexpressing EspH. EspH transiently expressed by the COS cells was localized to the membrane and disrupted the actin cytoskeletal structure. Our findings indicate that EspH is a modulator of the host actin cytoskeleton structure.     

Elevated levels of intrachromosomal homologous recombination in Arabidopsis overexpressing the MIM gene

The Arabidopsis MIM gene encodes a protein belonging to the SMC family (structure maintenance of chromosomes) which is required for intrachromosomal homologous recombination (ICR). Both ICR and MIM gene expression are enhanced by DNA-damaging treatments, suggesting that MIM is a factor limiting DNA repair by homologous recombination (HR) under genotoxic stress. We tested this hypothesis by measuring the levels of recombination in the mim mutant under genotoxic stress, using methyl methanesulfonate. Although the mutant clearly showed diminished basal and induced levels of ICR, enhancement of ICR by DNA-damaging treatments was similar to that observed in the wild type. This suggests that the MIM gene product is required for DNA repair by HR, but is not critical for HR induction. To determine whether enhanced availability of MIM would increase basal HR levels in Arabidopsis, we examined ICR frequencies in transgenic Arabidopsis strains overexpressing the MIM gene after ectopic insertion of additional MIM copies. Two independent lines showed a twofold increase in ICR frequency relative to the wild type. Thus MIM is required for efficient ICR in plants, and its manipulation can be used to change homologous recombination frequencies. Since MIM is one of the components responsible for chromatin dynamics, our results suggest that the chromatin environment determines the frequency of homologous recombination.     

Combinatorics of giant hexagonal bilayer hemoglobins

The paper discusses combinatorial and probabilistic models allowing to characterize various aspects of spacial symmetry and structural heterogeneity of the giant hexagonal bilayer hemoglobins (HBL Hb). Linker-dodecamer configurations of HBL are described for two and four linker types (occurring in the two most studied HBL Hb of Arenicola and Lumbricus, respectively), and the most probable configurations are found. It is shown that, for HBL with marked dodecamers, the number of 'normal-marked' pairs of dodecamers in homological position follows a binomial distribution. The group of symmetries of the dodecamer substructure of HBL is identified with the dihedral group D6. Under natural symmetry assumptions, the total dipole moment of the dodecamer substructure of HBL is shown to be zero. Biological implications of the mathematical findings are discussed.     

Ovalbumin increases macromolecular efflux from the in situ nasal mucosa of allergic hamsters

Gao, Xiao-Pei, Syed R. Akhter, and Israel Rubinstein.Ovalbumin increases macromolecular efflux from the in situ nasal mucosa of allergic hamsters. J. Appl.Physiol. 84(1): 169-176, 1998.The purpose ofthis study was to determine whether bradykinin mediatesovalbumin-induced increase in macromolecular efflux from the nasalmucosa of ovalbumin-sensitized hamsters in vivo and, if so, whether theL-arginine/nitric oxidebiosynthetic pathway transduces, in part, this response. We found thatsuffusion of ovalbumin onto the in situ nasal mucosa ofovalbumin-sensitized hamsters, but not of controls, elicited asignificant time- and concentration-dependent increase in clearance offluorescein isothiocyanate-labeled dextran (mol mass, 70 kDa;P < 0.05). HOE-140, but notdes-Arg⁹,[Leu⁸]-bradykinin,andN^G-L-argininemethyl ester (L-NAME), but notN^G-D-argininemethyl ester, significantly attenuated ovalbumin-induced responses.L-Arginine, but notD-arginine, abolished the effects ofL-NAME.L-NAME also significantlyattenuated bradykinin-, but not adenosine- induced increase inmacromolecular efflux from the in situ nasal mucosa. Overall, thesedata suggest that ovalbumin increases macromolecular efflux from the insitu nasal mucosa of ovalbumin-sensitized hamsters, in part, byproducing bradykinin with subsequent activation of theL-arginine/nitric oxidebiosynthetic pathway.